This study is a follow-on, open-label extension of a double-blind study. For subjects who achieved gabapentin monotherapy during the double-blind study, the purpose of this study is to evaluate long term safety of gabapentin. For subjects who did not achieve gabapentin monotherapy during the double-blind protocol, the objectives are to evaluate long term safety of gabapentin and to determine the percentage of patients who achieve gabapentin monotherapy in this study.